1. Field of the Disclosure
Embodiments disclosed herein relate generally to drilling rigs. In particular, embodiments disclosed herein relate to drilling rig assembly methods and apparatus.
2. Background Art
A drilling rig is used to drill a wellbore in a formation. Drilling rigs may be large structures that house equipment used to drill water wells, oil wells, or natural gas extraction wells. Drilling rigs sample sub-surface mineral deposits, test rock, soil and groundwater physical properties, and may also be used to install sub-surface fabrications, such as underground utilities, instrumentation, tunnels or wells. Drilling rigs may be mobile equipment mounted on trucks, tracks, or trailers, or more permanent land or marine-based structures (such as oil platforms). The term “rig,” therefore, generally refers to a complex of equipment that is used to penetrate the surface of the earth's crust.
Referring to FIG. 1, a conventional drilling rig 30 is shown. Drilling rig 30 includes a derrick 14, which provides a support structure for a majority of the equipment used to raise and lower a drillstring 25 into and out of a wellbore. The drillstring 25 may be an assembled collection of drillpipe, drill collars, or any other assortment of tools, connected together and run into the wellbore to facilitate the drilling of a well (drillpipe 16 is shown in joints prior to being connected together). The drillstring 25 may be raised and lower into and out of the wellbore by the draw-works 7, which includes a spool powered by a motor or other power source 5. A drill line 12, which may be a thick, stranded metal cable, is run from the draw-works 7 over a crown block 13 and down through a travelling block 11. Typically, the crown block 13 remains stationary while the travelling block 11 moves vertically with the drillstring 25. The combination of the crown block 13 and the travelling block 11 provides a significant mechanical advantage for lifting the drillstring 25. Further, a swivel 18 may be attached to the travelling block 11 to allow rotation of the drillstring 25 without twisting the travelling block 11.
The drilling rig 30 further includes a rotary table 20 mounted in a rig floor 21, which is used to rotate the drillstring 25 along with a kelly drive 19. Kelly drive 19, attached at an upper end to the swivel 18 and at a lower end to the drillstring 25, is inserted through the rotary table 20 to rotate the drillstring 25 (drillstring rotation shown by arrow “R”). Kelly drive 19 may be square, hexagonal, or any other polygonal-shaped tubing and is able to move freely vertically while the rotary table 20 rotates it. Alternatively, drilling rig 30 may include a top drive (not shown) in place of kelly drive 19 and rotary table 20. Additionally, blowout preventers (“BOPs”) may be located below the rig floor 21 and installed atop a wellhead 27 to prevent fluids and gases from escaping from the wellbore. An annular BOP 23 and one or more ram BOPs 24 are shown and are commonly understood in the art.
During drilling operations, drilling fluid may be circulated through the system to carry cuttings away from the bottom of the wellbore as drilling progresses. Drilling fluid may be stored in mud tanks 1 before being drawn through suction line 3 by mud pumps 4. Drilling fluid (drilling fluid route is indicated by arrows “F”) is then pumped from mud pumps 4 through a hose 6, up a stand pipe 8, through a flexible hose 9, and down into the wellbore. Drilling fluid returning from the wellbore is routed through a flow line 28 to shakers 2, which are used to separate drill cuttings from the drilling fluid before it is pumped back down the wellbore.
When designing a drilling rig, numerous factors may be taken into account. For instance, referring still to FIG. 1, the crown block 13 must be located high enough to pull the drillstring 25 from the wellbore for assembly or disassembly. This may require that the derrick structure 14 be built having a substantial height to have the crown block 13 high enough above the wellbore. Additionally, the rig floor 21 must be high enough off the ground to allow the blowout prevention equipment, namely BOPs 23, 24, to fit beneath the rig floor 21 when mounted on the wellhead 27. Due to these design factors, among others, the size of drilling rigs is often very large. Due to the large size, assembly of the drilling rigs may often be difficult.
Different methods have been employed to assemble drilling rigs and attempt to overcome the difficulty associated with assembling very large structures having on them a substantial amount of drilling equipment. One method used is known as “box on box,” which basically uses a crane to stack large box structures on top of one another up to a certain height. The crane is then used to lift the rig floor onto the stacked boxes. After the rig floor is installed, the remaining equipment, including the derrick and blocks, must be assembled. One drawback to this assembly method is that a substantial crane is required to lift the equipment during assembly, which due to often rough terrain in remote drilling locations becomes extremely costly or even unfeasible in certain conditions. Also, assembly of a majority of the drilling equipment occurs after the rig floor is installed, and thus, must take place at the rig floor height, which may be 25-40 feet (8-12 m) off the ground.
Other methods used to assemble drilling rigs are known as “swing up,” “slingshot,” or some other form of parallelogram method. Using any of these methods, the drilling rig is, in a sense, collapsed because the rig floor sits on a base near the ground with the legs laid out horizontal. A hydraulic or wireline system then pulls the structure up (the rig floor is lifted off the ground and the legs are raised to a vertical position). However, these assembly methods typically incur unusually high loads, which may increase chances of mechanical failure. Additionally, active participation of rig personnel is required during assembly. Accordingly, there exists a need for a method and apparatus for a drilling rig capable of being assembled with minimal extra equipment (e.g., cranes) and minimal rig personnel participation during assembly.